SP4490 Datasheet, PDF (5/12 Pages) Sipex Corporation – Two Panel Electroluminscent Lamp Driver

VBATT
C1
0.1µF
EL1/EL2
ON/OFF
ROSC
464kΩ
C2*
10nF
1
4
VDD
2
ROSC
3
SP4490
10 8
EL1 ELcommon
6
COIL
7
CAP
5
VSS
9
EL2
* optional device
L1
470µH
D1
1N4148
CINT
1800pF
EL Lamp
Figure 2: Typical Application Circuit of SP4490
EL Lamp
Electroluminescent backlighting is ideal when
used with LCD displays, keypads or other back-
lit readouts. EL lamps uniformly light an area
without creating any undesirable "hot spots" in
the display. Also, an EL lamp typically con-
sumes less power that LED's or incandescent
bulbs in similar lighting situations. These fea-
tures make EL ideal for attractive, battery pow-
coil switch is on, the coil is connected between
V and coil switch and a magnetic field devel-
DD
ops in the coil. When the coil switch turns off,
the switch opens, the magnetic field collapses
and the voltage across the coil rises. The internal
diode forward biases when the coil voltage rises
above the H-Bridge voltage and the energy en-
ters the EL lamp. Each pulse increases the
ered products.
THEORY OF OPERATION
As the voltage approaches its maximum, the
steps become smaller. (see figure 4).
Coil Switch
The SP4490 has an inductor-based boost con-
verter to generate the high voltage used to drive
the EL lamp. Energy is stored in the inductor
according to the equation E = 1/2 (LI ²) where
L
pk
I_pk = (t_ON) (V_BATT - V_CEsat) /L. An internal oscilla-
tor controls the coil switch. During the time the
coil switch is on, the coil is connected between
V_DD and the saturation voltage of the
The brightness of the EL lamp output is directly
related to energy recovery in the boost converter.
There are many variations among coils such as
magnetic core differences, winding differences
and parasitic capacitances. For suggested coil
suppliers refer to page 10.
Oscillator
The internal oscillator generates a high frequency
clock used by the boost converter and H-
Rev. 9/12/00
SP4490 Two Panel Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
5